The Environmental Protection Agency (EPA) released a public letter on Mon. Apr 22 criticizing the conclusions of a Mar. 1, 2013 State Department environmental review of the proposed Keystone XL tar sand pipeline.

The EPA letter criticized those findings, arguing that the State Department report did not properly assess the higher costs associated with rail transport of tar sand oil. The EPA reasoned that higher transportation costs could reduce the total amount of tar sands oil that is extracted and refined, thus reducing future greenhouse gas emissions.

Jack Spencer, Senior Research Fellow at the Heritage Foundation, challenged the EPA's conclusions stating that the "EPA’s objections to the State Department’s draft [environmental impact statement] demonstrate once again that the EPA is more interested in promoting a political agenda than protecting public health and safety… The XL pipeline has been studied extensively and has been found to be environmentally safe twice."

Senator Bernie Sanders (I-VT) has been opposed to the pipeline stating that he is "disturbed by the proposal" and questions "why in the world would we ever consider approving a new Big Oil pipeline to carry dirty fuel and keep America addicted to oil, when we could save money, create jobs, and reduce our dependence on foreign oil by moving to stronger fuel economy standards?" Dr. James Hansen, former Director of the Goddard Institute for Space Studies at NASA, has argued that "exploitation of tar sands would make it implausible to stabilize climate and avoid disastrous global climate impacts."

However, the US Chamber of Commerce states that approving the pipeline will "provide approximately twenty thousand badly needed manufacturing and construction jobs, and contribute an estimated $20 billion in benefits to the U.S. economy." The National Petrochemical and Refiners Association has argued that "limiting oil sands crude use could cause Canadian producers to ship their product to Asian markets, while the US would have to import more oil in tankers from the Middle East and elsewhere, thus increasing the carbon footprint."

If the Keystone XL pipeline is approved it could eventually transport up to 830,000 barrels of diluted bitumen crude (tar sand oil) over 1,700 miles from Alberta, Canada to refineries in Texas. According to the EPA, tar sand oil can emit up to 82% more carbon dioxide than conventional oil.